Topspin,
I just read the book and Allen Fox does highly recommend moving forward as you volley with these quotes "Movement,then,is an intrinsic part
of the volley stroke. On a volley, you generally hit from a moving
platform. Since the volleyer will be moving forward at a relatively
high velocity when he hits the ball. Under match conditions,volleys
are hit while moving,integrating the eyes,hands, and legs in the
stroke. Yet ,like a pianist practicing an improper sequence of notes
most players practice the volley while standing still or taking just one mechanical step."
This book is excellent and should be a must read for all levels of
tennis players.